Qualité microbiologique des tranches de mangues (Mangifera indica L.) vendues à Dakar (Sénégal)

La mangue, principal fruit du Sénégal, est transformée en tranches et vendue en sachets dans les rues de Dakar. Ce produit est sensible aux altérations microbiennes faute de technologies de conservation adaptées au contexte local. Ce travail propose une évaluation de la qualité  microbiologique du produit et de son impact sur la santé des  consommateurs. Pour cette étude, 3 répétitions d’échantillons par vendeur ont été prélevées chez quatorze vendeurs de cinq quartiers (Médina, Fann, Habitats Loyers Modernes ou HLM, Grand Yoff et Guédiawaye). Ensuite, des analyses ont été menées pour la recherche de la flore mésophile aérobie totale, de coliformes, d’entérobactéries et d’Escherichia coli présomptifs. Les résultats montrent une forte pollution des échantillons en flore totale sauf pour l’échantillon V3 (vendeur 3) des HLM et une charge élevée en coliformes et en Escherichia coli (> 103 UFC/g). D’autres entérobactéries comme Enterobacter agglomerans, Enterobacter amnigenus, Serrati  rubidaea et Klebsiella pneumoniae sont retrouvées respectivement dans les échantillons V2 de Médina, V1 de Fann, V1 et V2 Guédiawaye. Ces bactéries ne présentent pas de risques sur la santé publique mais rendent le produit impropre à la consommation. Cette étude nécessite une expansion aux autres quartiers pour mieux veiller sur la santé des consommateurs.Mots clés: Evaluation, qualité, microbiologie, mangues, santé des consommateurs, Dakar

Use of edible and biodegradable coatings in fresh cut pineapple.

The use of edible coatings in vegetable products has been increasing because it offers several advantages as being biodegradable and extends the shelf-life of fruits and vegetables. The objective of this work was to evaluate the effect of two biodegradable edible coatings, sodiumalginate and Chitosan, on the quality and shelf life of minimally processed pineapple storage at 10°C. Five L of each coating solutions were prepared as following - 2% alginate solution: 100 g of Algenic acid sodium salt in 5 L of distilled water, heated at 70°C under constant stirring - 0,75% Chitosan solution: 150 g of monohydrated citric acid dispersed in 5 L of distilled water and addition 37.5g of Chitosan (Crab shells Chitosan, minimum 85% deacetylated, SIGMA), heated to 60°C to dissolve the Chitosan. The coating solutions were then stored at 5°C before the dipping. The Chitosan coating had an important benefic effect on the microbiological contamination and on the maintenance of the total phenolic content. The high concentration of citric acid in the coating solution contributed to the antimicrobial effect but changed the sensory taste of fresh pineapple. The alginate coating also decreased the contamination of yeasts and molds but its effect was lower than the Chitosan one. Visual aspect of its coating solution can be not well accepted by the consumers. The concentration of alginate must be decreased to avoid the formation of a too thick gel. The Chitosan treatment resulted in the best product at the end of experiment and the most slight decreasing of phenolic compounds during all the experiments

Towards the understanding of the cocoa transcriptome: Production and analysis of an exhaustive dataset of ESTs of Theobroma cacao L. generated from various tissues and under various conditions

Theobroma cacao L., is a tree originated from the tropical rainforest of South America. It is one of the major cash crops for many tropical countries. T. cacao is mainly produced on smallholdings, providing resources for 14 million farmers. Disease resistance and T. cacao quality improvement are two important challenges for all actors of cocoa and chocolate production. T. cacao is seriously affected by pests and fungal diseases, responsible for more than 40% yield losses and quality improvement, nutritional and organoleptic, is also important for consumers. An international collaboration was formed to develop an EST genomic resource database for cacao. Fifty-six cDNA libraries were constructed from different organs, different genotypes and different environmental conditions. A total of 149,650 valid EST sequences were generated corresponding to 48,594 unigenes, 12,692 contigs and 35,902 singletons. A total of 29,849 unigenes shared significant homology with public sequences from other species. Gene Ontology (GO) annotation was applied to distribute the ESTs among the main GO categories. A specific information system (ESTtik) was constructed to process, store and manage this EST collection allowing the user to query a database. To check the representativeness of our EST collection, we looked for the genes known to be involved in two different metabolic pathways extensively studied in other plant species and important for T. cacao qualities: the flavonoid and the terpene pathways. Most of the enzymes described in other crops for these two metabolic pathways were found in our EST collection. A large collection of new genetic markers was provided by this ESTs collection. This EST collection displays a good representation of the T. cacao transcriptome, suitable for analysis of biochemical pathways based on oligonucleotide microarrays derived from these ESTs. It will provide numerous genetic markers that will allow the construction of a high density gene map of T. cacao. This EST collection represents a unique and important molecular resource for T. cacao study and improvement, facilitating the discovery of candidate genes for important T. cacao trait variation. (Résumé d'auteur

Melting of hybrid organic-inorganic perovskites.

Several organic-inorganic hybrid materials from the metal-organic framework (MOF) family have been shown to form stable liquids at high temperatures. Quenching then results in the formation of melt-quenched MOF glasses that retain the three-dimensional coordination bonding of the crystalline phase. These hybrid glasses have intriguing properties and could find practical applications, yet the melt-quench phenomenon has so far remained limited to a few MOF structures. Here we turn to hybrid organic-inorganic perovskites-which occupy a prominent position within materials chemistry owing to their functional properties such as ion transport, photoconductivity, ferroelectricity and multiferroicity-and show that a series of dicyanamide-based hybrid organic-inorganic perovskites undergo melting. Our combined experimental-computational approach demonstrates that, on quenching, they form glasses that largely retain their solid-state inorganic-organic connectivity. The resulting materials show very low thermal conductivities (~0.2 W m-1 K-1), moderate electrical conductivities (10-3-10-5 S m-1) and polymer-like thermomechanical properties

ESKIMO1 Disruption in Arabidopsis Alters Vascular Tissue and Impairs Water Transport

Water economy in agricultural practices is an issue that is being addressed through studies aimed at understanding both plant water-use efficiency (WUE), i.e. biomass produced per water consumed, and responses to water shortage. In the model species Arabidopsis thaliana, the ESKIMO1 (ESK1) gene has been described as involved in freezing, cold and salt tolerance as well as in water economy: esk1 mutants have very low evapo-transpiration rates and high water-use efficiency. In order to establish ESK1 function, detailed characterization of esk1 mutants has been carried out. The stress hormone ABA (abscisic acid) was present at high levels in esk1 compared to wild type, nevertheless, the weak water loss of esk1 was independent of stomata closure through ABA biosynthesis, as combining mutant in this pathway with esk1 led to additive phenotypes. Measurement of root hydraulic conductivity suggests that the esk1 vegetative apparatus suffers water deficit due to a defect in water transport. ESK1 promoter-driven reporter gene expression was observed in xylem and fibers, the vascular tissue responsible for the transport of water and mineral nutrients from the soil to the shoots, via the roots. Moreover, in cross sections of hypocotyls, roots and stems, esk1 xylem vessels were collapsed. Finally, using Fourier-Transform Infrared (FTIR) spectroscopy, severe chemical modifications of xylem cell wall composition were highlighted in the esk1 mutants. Taken together our findings show that ESK1 is necessary for the production of functional xylem vessels, through its implication in the laying down of secondary cell wall components